This invention relates generally to image sensors, and more particularly to an integrated image sensor using micromirrors.
Security is an increasing concern for governments, industry and individuals alike. The use of passwords has many associated problems. Passwords are changed on a regular basis inducing password fatigue. Password fatigue is evident in the choice of banal passwords, for example, names of children or dogs, dates of birth etc. Obviously, such simple passwords present a security risk. In addition, the use of computer algorithms for breaking passwords is an increasing problem.
In light of the problems associated with passwords, biometric sensing is becoming increasingly used. One important type of biometric sensing exploits the unique topography of an individual""s skin to allow or deny access. The most commonly used skin for biometric sensing is on the fingertip. The fingerprint is widely accepted around the world as proof of identity. It is widely understood that fingerprints are unique to each individual and essentially impossible to lose. In contrast to digital signatures, fingerprints have proven legal standing. In fact, the fingerprint is used in situations where there can be no mistake, such as in criminal proceedings and high-security access. In comparison to other biometric methods, such as retinal scans, a fingerprint scan is non-intrusive.
In an optical fingerprint input transducer or sensor, the finger under investigation is usually pressed against a flat surface, a platen, such as a side of a glass plate, and the ridge and valley pattern of the finger tip is sensed by a sensing means such as an interrogating light beam. Various optical devices are known which employ prisms upon which a finger whose print is to be identified is placed. The prism has a first surface, the platen, upon which a finger is placed, a second surface disposed at an acute angle to the first surface through which the fingerprint is viewed and a third illumination surface through which light is directed into the prism. In some cases, the illumination surface is at an acute angle to the first surface, as seen for example, in U.S. Pat. Nos. 5,187,482 and 5,187,748. In other cases, the illumination surface is parallel to the first surface, as seen for example, in U.S. Pat. Nos. 5,109,427 and 5,233,404. Fingerprint identification devices of this type are generally used to control the building-access or information-access of individuals to buildings, rooms, and devices such as computer terminals. However, in the prior art discussed above the light after interrogation of a surface must be xe2x80x9cobservedxe2x80x9d by an image sensor, which is typically a charge coupled device (CCD) array. Generally, the most expensive component in an optical imager is the image sensor.
It has now been found that it is possible to reduce the image sensor area. By reducing image sensor area in an optical imager, it is now possible to reduce the component costs of the image sensor required for an optical imager. Conversely, it is also possible to retain current image sensor area and to significantly increase resolution of images captured therewith.
Thus, in an attempt to overcome these and other limitations of prior art devices, it is an object of this invention to provide an efficient use of image sensor area.
Thus, in accordance with the present invention there is provided an optical imager comprising: a light source for emitting light; a platen for reflecting a portion of light emitted by the light source and incident thereon; an image sensor for sensing light incident thereon; and, a micromirror device operable from a first reflecting position to a second other reflecting position, the micromirror device for reflecting light reflected by the platen along a first optical path in a first reflecting position such that a first portion of light reflected from the platen is incident on the image sensor and for reflecting light reflected by the platen along a second optical path in a second reflecting position such that a second portion of light reflected from the platen is incident on the image sensor, wherein the first portion of light and the second portion of light are reflected from different positions of the platen.
In accordance with the invention there is further provided a method of capturing an image comprising the steps of: positioning an array of micromirrors in a first reflective position; acquiring a first image of light reflected from the array of micromirrors to form an image of a first area; positioning the micromirrors in a second other reflective position; acquiring a second image of light reflected from the array of micromirrors to form an image of a second area; and, combining the first image and the second image to form a composite image of an area larger than the first area and larger than the second area.
In accordance with another aspect of the invention there is provided a method of capturing an image comprising the steps of positioning an array of micromirrors in a first reflective position; acquiring a first image of light reflected from the array of micromirrors to form an image of a first area; moving the micromirrors to a second other reflective position; during motion of the micromirrors at intervals acquiring a plurality of images of light reflected from the array of micromirrors to form an image of a other areas; and, combining the first image and the plurality of images to form a composite image.